Disclosed in JP3114647B is a brake system for a behavior control of a vehicle, that “includes a means for detecting a steering angle and a means for detecting a steering angular velocity and that starts actuating a pump means when a degree (a level) of the steering angle becomes equal to or greater than a reference value of the steering angle and when a level of the steering angular velocity becomes equal to or greater than a reference value of the steering angular velocity” in order to “ensure a favorable responsiveness of a behavior control by means of a braking force in a manner where the pump means is actuated at a stage where a condition of inducing a deterioration of a vehicle behavior is satisfied, instead of actuating the pump means at a stage where the vehicle behavior is actually deteriorated to some extent”.
Disclosed in JP4119244A is a method for regulating a driving stability of a vehicle that “determines whether or not the vehicle is inclined to be in an unstable traveling condition from a stabile traveling condition on the basis of an abrupt (sudden) steering operation (a start of the steering operation)” and that allows “a preliminary brake intervention” to be executed on the basis of a maximum value of a steering wheel angular velocity and the like in order to “execute the preliminary brake intervention while the vehicle stably travels in the case where the vehicle is determined to incline to be in the unstable driving condition when a driver performs the sudden; steering performance”.
Disclosed in JP2007-513002T states that “a brake pressure is likely to increase while a vehicle travels on a road having a limited inclination. Therefore, a desired target brake torque starts acting on the vehicle only after a predetermined time, which is used as a function for a brake apparatus, has been passed. This delay time (i.e. a delay of the brake pressure in acting on the vehicle) may result in generating a sideslip at the vehicle, and the vehicle may not sufficiently and promptly be stabilized in highly dynamic maneuvers.” Furthermore, the regulation of driving dynamics disclosed in JP2007-513002T “determines a lateral acceleration of the vehicle and a steering speed and monitors the lateral acceleration and the steering speed in relation to threshold values, so that a preparatory brake pressure is built up in a case where the lateral acceleration exceeds a threshold value and the steering speed falls below a threshold value” in order to “promptly stabilize the vehicle while the vehicle is in a dangerous driving state”.
The above-mentioned specifications (JP3114647B, JP4119244B and JP2007-513002T), for example, estimate a start of an execution of a vehicle stability control on the basis of the steering angular velocity and the like in a situation where the driver needs to abruptly and emergently avoid an obstacle while driving, and then, execute a control for applying an auxiliary brake torque to the vehicle in order to compensate a responsiveness of an actuator before the vehicle stabilizing control is executed (this control will be hereinafter referred to as a preparatory control). More specifically, a brake torque in a low level is applied to the vehicle in the preparatory control. Generally, a noise and a vibration are likely to be generated when the actuator is actuated. Therefore, in a case where the vehicle stabilizing control is not executed even if the preparatory control is executed, the noise and the vibration may cause a discomfort to the driver. Generally, an auxiliary pressure control (i.e. the preparatory control, a control for generating an auxiliary (preparatory) pressure) may be needed in a case where changes in the vehicle behavior are abrupt. However, in a case where changes in a yawing behavior are slow and gradual (e.g. in a case where an understeering tendency occurs at the vehicle), the auxiliary pressure control may not be needed.
A need thus exists to provide a motion control device for a vehicle for properly executing a vehicle stabilizing control while avoiding an unnecessary execution of an auxiliary pressure control (a preparatory control) and avoiding a generation of discomfort to a driver.